Self-powered long-life occupancy sensors and sensor circuits

ABSTRACT

Occupancy sensors are provided that do not require an external power source in order to operate. The sensors operate with a low voltage non-rechargeable battery and are fully functional for at least about 15-20 years. The sensors include a relay output capable of switching high or low voltage and high or low current with virtually no generated heat. The sensors require no warm-up period, no minimum load, and no external ground connection. The sensors are always active and are easily installed, having two electrically interchangeable outputs for coupling to, for example, a load and a load power source.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 10/144,450, filedMay 10, 2002, now U.S. Pat. No. 6,850,159, which claims the benefit ofU.S. Provisional Application No. 60/291,188, filed May 15, 2001, both ofwhich are hereby incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

This invention relates to occupancy sensors. More particularly, thisinvention relates to occupancy sensors that can operate for extendedperiods of time without an external power source.

Occupancy sensors typically sense the presence of one or more personswithin a designated area and generate occupancy signals indicative ofthat presence. Such occupancy signals may then drive, for example, a lowvoltage transformer and relay to activate or deactivate one or moreelectrical devices or appliances, such as, for example, room lighting oran HVAC (heating, ventilating, and air conditioning) system. Occupancysensors help reduce energy and maintenance costs by turning devices andappliances OFF when not needed.

Accordingly, occupancy sensors are typically used in a variety ofcommercial, industrial, and residential settings. Most known occupancysensors require an external power source in order to operate. That is,they require a connection to an external power source in order to powersensing, timing, and switching circuits that turn lights or otherdevices ON and OFF in accordance with sensed occupancy. Thus, adisadvantage of most known sensors is that they cannot be used in areaswhere power is not readily available.

Furthermore, the settings mentioned above typically have differentelectrical environments. For example, some settings have AC line voltagethat may be 120, 240, 277, or 347 volts. Other settings may have only DCvoltage supplies available. Another disadvantage of known occupancysensors is that they typically can operate only within a narrow range ofeither AC or DC input voltage. For example, many known sensors can onlyoperate at 120 volts AC. Such sensors are not likely to operate at, forexample, 12 volts DC or 240 volts AC. Similarly, an occupancy sensorthat can operate at 24 volts DC, cannot likely operate at an AC linevoltage of 347 volts. Thus, known occupancy sensors are generallylimited to a particular input voltage range and type (AC or DC). Suchvoltage limitations can significantly limit the types of applications inwhich known occupancy sensors can be used.

Another disadvantage of known occupancy sensors is that they often wastepower in standby mode (i.e., when the sensor is not sensing occupancy).Power is wasted because known occupancy sensors continuously drawcurrent. Often, this continuously drawn current is set to the peakcurrent of the sensor. Peak current, however, is only required whenoccupancy is sensed, which is when most circuit activity occurs. Thus,more power than necessary is often dissipated (and thus wasted) in knownsensors. This can become notable, for example, in an office complexwhere dozens of such sensors are deployed.

Moreover, unnecessary power dissipation is usually higher in knownoccupancy sensors with relay outputs. Relay outputs advantageously allowa sensor to be used in many different types of applications. However,relay outputs typically consume relatively large amounts of current.Sensors with relay outputs include a relay coil that is energized andde-energized as needed to switch the relay output to either couple powerto a load (i.e., a device or appliance to be turned ON/OFF by thesensor) or decouple power from the load. Many known sensors maintain thecoil in an energized state while in standby mode. This significantlyincreases power dissipation.

Another disadvantage of known occupancy sensors is that they are easilymis-wired during installation. Most sensors have wires for connection tothe hot, neutral, and ground leads of a power source, and other wiresfor connection to a load and power source for the load (if differentfrom the power source for the sensor). Wiring mistakes are common,typically causing installation delays and malfunctioning sensors, whichmay not always be immediately detected.

A further disadvantage of known occupancy sensors is that they usuallyrequire a warm-up period upon initial installation and after poweroutages. This also can delay installation because installers need towait until warm-up is complete in order to ensure that sensors arefunctioning properly. Warm-up periods after power outages can also wastepower because many known sensors warm up in the ON state. Thus, forexample, lighting for a manufacturing floor may turn ON after power isrestored at a time when no one is present. Conversely, other knownsensors that warm up in the OFF state can further disrupt productivityafter a power outage. For example, an occupied area may remain withoutlights or HVAC for the duration of the warm-up period after power isrestored.

A few known occupancy sensors power some functions with a battery. Forexample, some sensors use the battery as backup in case of a poweroutage, to store data for later downloading to a computer, or totransmit a signal to a remote receiver. Battery-operated occupancysensors, however, are not known to use a battery to operate a relayoutput which, as mentioned above, advantageously increases theversatility of the sensor. Furthermore, known battery-operated occupancysensors typically cannot operate at extended periods of time withoutreplacing the battery, thus maintenance costs may be higher for suchsensors.

Some known occupancy sensors operate with rechargeable batteries. Thesesensors have additional disadvantages. For example, rechargeablebatteries are usually more expensive than non-rechargeable batteries,have more internal leakage resulting in more rapid capacity loss, oftenrequire 24-48 hours of initial charging before the sensor is fullyoperational, typically require connection to a load in order to remainfully operational (the batteries leak current through the load while theload is off), and typically require a current transformer in series withthe load in order to re-charge while the load is powered.

In view of the foregoing, it would be desirable to be able to provide anoccupancy sensor that can operate for many years without an externalpower source.

It would also be desirable to be able to provide an occupancy sensorwith a relay output that can operate for many years without an externalpower source.

It would further be desirable to be able to provide an occupancy sensorthat dissipates very little power.

It would still further be desirable to be able to provide an occupancysensor that is easily installed.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an occupancy sensor thatcan operate for many years without an external power source.

It is also an object of this invention to provide an occupancy sensorwith a relay output that can operate for many years without an externalpower source.

It is a further object of this invention to provide an occupancy sensorthat dissipates very little power.

It is still a further object of this invention to provide an occupancysensor that is easily installed.

In accordance with this invention, an occupancy sensor with a relayoutput is provided that does not require an external power source.Instead, the sensor is powered internally by an energy storage device,which is preferably a non-rechargeable preferably single-cell battery.The self-powered occupancy sensor can operate for extended periods oftime (e.g., about 15-20 or more years) without replacement of the energystorage device. Moreover, the sensor does not require a warm-up periodor connection to a load in order to be fully functional, nor does itrequire a current transformer to remain fully functional. Circuits ofthe self-powered occupancy sensor draw negligible, if any, current instandby mode and very small amounts of current during occupancydetection and switching of the relay output. Moreover, installation ofthe sensor is very easy, if not foolproof, requiring only twoelectrically interchangeable connections, one to a load and the other toa load power supply. No external connection to ground is required.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages of the invention will beapparent upon consideration of the following detailed description, takenin conjunction with the accompanying drawings, in which like referencecharacters refer to like parts throughout, and in which:

FIG. 1 is a perspective view of an exemplary embodiment of aself-powered occupancy sensor according to the invention;

FIG. 2 is a block diagram of an exemplary embodiment of a self-poweredoccupancy sensor according to the invention; and

FIGS. 3-9 are circuit diagrams of exemplary embodiments of sensorcircuits according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a self-powered occupancy sensor that has a verylong operating life of preferably about 20 years or more. Theself-powered sensor includes a relay output that does not rely onvoltage from an installation site. The relay output can switch largecurrents (with little generated heat) as well as very low currents suchas those in signaling circuits. Thus, the self-powered sensor can beadvantageously installed world wide regardless of local voltages andwiring. The sensor also can be advantageously used with many differenttypes of devices and equipment including, for example, energy managementsystems (even open collector), solar powered devices, and otherbattery-operated equipment. Moreover, the sensor can be installed inremote areas with no available power for use with, for example, wirelessdevices and transmitters.

The self-powered occupancy sensor is enclosed in a housing havingpreferably only two external electrical conductors connected internallyto the relay contacts. The two conductors are advantageouslyinterchangeable and can be connected externally to, for example, a loadand a load power source. Thus, the possibility of mis-wiring theconductors to the “hot” and “load” leads is substantially reduced, ifnot eliminated. Advantageously, because the sensor is self-powered, anexternally connected ground wire is not required. Moreover, the sensoris always on and immune to utility power outages, and has no minimumload requirements.

FIG. 1 shows an embodiment of a self-powered occupancy sensor inaccordance with the invention. Sensor 100 has a housing 102 dimensionedto enclose sensor circuits and an energy storage device (e.g., one ormore batteries). Sensor 100 advantageously has only two wires 104 and106 external to housing 102 that can be connected to a load (i.e., anelectrical device or appliance whose ON/OFF state is controlled by thesensor) and a power source for the load. Advantageously, wires 104 and106 can be interchangeably connected to the load and power sourcewithout adversely affecting the operation of the sensor or the load.That is, wire 104 can be connected to either the load or power sourcewhile wire 106 can be connected to the power source or load. Sensor 100is preferably sized to be installed in a single gang switch box. Thus,it can replace a standard wall switch. Sensor 100 also preferablyincludes an optional Fresnel lens 108, an optional LED 110, and anoptional manual override switch 112. Switch 112 preferably slides up anddown and can be set in the AUTO (i.e., automatic) position for normaloperation or in the OFF position to deactivate occupancy sensing.

FIG. 2 shows an embodiment of a self-powered occupancy sensor inaccordance with the invention. Sensor 200 preferably includes housing202, outputs 204 and 206, relay output circuit 214, relay driver 216,sensing circuit 218, timer 220, and energy storage device circuit 222.Energy storage device circuit 222 is configured to receive an energystorage device 224, which powers sensor 200 and is completely containedwithin housing 202. Energy storage device 224 is preferably anon-rechargeable single-cell battery, but can be other devices thatperform similarly, as described further below. Energy storage device 224can be installed either during manufacturing and assembly of the sensoror thereafter. And although not intended to require regular replacing orservicing, an optional removable or hinged door (not shown) in housing202, as is known in the art of other battery-operated devices, can beprovided to install and remove energy storage device 224.

Relay output circuit 214 has electrical conductors 204 and 206 connectedto relay contacts 205 and 207, respectively. Relay output circuit 214includes an armature for setting relay contacts 205 and 207 in either anopen-circuit state (i.e., no conductive path between contacts 205 and207 through relay output circuit 214) or a closed-circuit state (i.e., aconductive-path between contacts 205 and 207 through relay outputcircuit 214).

Relay driver 216 is a low power preferably latching relay circuit (e.g.,requiring about 10 msec of a 200 mW pulse) that consumes virtually zerocurrent in standby mode and very little current from energy storagedevice 224 when producing pulses to transfer relay output 214 from onestate to the other. Relay driver 216 includes a relay coil andpreferably operates with voltages ranging from about 3.6 volts to about2.4 volts or less.

Sensing circuit 218 preferably includes passive infrared (PIR)technology to sense occupancy within a designated area. PIR technologysenses the difference between the heat generated by the designated areaand the heat generated by a person entering that area, and generallyresults in less false-tripping than other sensing technologies.Alternatively, however, sensing circuit 218 can include other sensingtechnologies such as, for example, ultrasonic sensing, photoelectricsensing, sound sensing, or any combination thereof, now known or laterdeveloped, provided that their power requirements are substantiallysimilar to that of PIR technology.

Sensing circuit 218 also preferably includes a two-stage operationalamplifier circuit that preferably requires only several microamps ofcurrent to operate. Alternatively, an appropriately designedsingle-stage amplifier circuit may be used instead. When occupancy issensed, sensing circuit 218 generates and amplifies an occupancy signal(e.g., a logical 1 signal, represented by a “high” or upper-railvoltage).

Timer 220 prevents the lights or other devices controlled by sensor 200from turning OFF during brief periods of non-occupancy. Timer 220preferably has selectable time periods and is activated by receipt of asignal indicating occupancy from sensing circuit 218. Receipt ofadditional occupancy signals during a selected time period resets thattime period. If no other occupancy signals are received, the lights orother devices will turn OFF upon expiration of the time period. Timer220 draws very little current when activated and virtually no current instandby mode.

In an alternative embodiment, timer 220 need not be included in sensor200. Occupancy signals generated by sensing circuit 218 can be insteadfed directly to relay driver 216.

FIGS. 3-9 show exemplary embodiments of circuits that can be used inself-powered long-life occupancy sensors constructed in accordance withthe invention. Circuits 300, 400, 500, 600, 700, 800, and 900 coupledtogether as indicated in FIGS. 3-9 form an exemplary embodiment of aself-powered long-life occupancy sensor in accordance with theinvention.

FIG. 3 shows an exemplary embodiment of a PIR sensing circuit inaccordance with the invention. Sensing circuit 300 preferably includesresistors R1-R15, capacitors C6-C10 and C13-C18, NPN transistors Q1 andQ2, PNP transistor Q3, piezoelectric chip Z1, and operational amplifiers(opamps) 326 and 328. Opamps 326 and 328 operate with very low current,requiring no more than about 15 microamperes each. Preferably, however,they require only about 7 microamperes each, and more preferably onlyabout 1 microampere each. Opamps 326 and 328 can be, for example,ultra-low power OPA2349 dual opamps, manufactured by Burr-Brown, ofTucson, Ariz. Alternative embodiments may only include one opamp, as isknown in the art. The overall current (and thus power) required by anoccupancy sensor of the invention is predominately determined by theopamp current.

Sensing circuit 300 operates preferably as follows: when temperature inan area sensed by an occupancy sensor of the invention increases (e.g.,when a person enters the area), chip Z1 generates a very small voltagewith high impedance. FET transistor 330, which is included in chip Z1and lowers the impedance to an acceptable level, outputs a signal atnode 331 indicating occupancy. The signal is amplified via two-stagebandpass amplifier 332. Resistor R12 ground references the signal fromopamp 328. If that signal goes positive by about 0.4 volts, transistorQ2 turns ON (i.e., conducts current). If the signal goes negative byabout 0.4 volts, transistor Q1 turns ON. If either or both transistorsQ1 and Q2 turn ON, Q3 also turns ON. This causes the collector oftransistor Q3 (node 333) to rise from the lower rail (e.g., the sensor'sinternal ground) to about the upper rail (e.g., V_(BAT)).

FIG. 4 shows an exemplary embodiment of a timer circuit in accordancewith the invention. Timer circuit 400 preferably includes resistorsR16-R23, optional capacitors C1 and C2, capacitors C3 and C19, optionalswitches SW1A and SW1B (to be used with optional capacitors C1 and C2),NPN Darlington pair Q4, NPN transistors Q5 and Q7, PNP transistors Q6and Q8, and optional photocell circuit 440.

Timer circuit 400 operates preferably as follows: when node 333 (i.e., anode that receives signals indicating occupancy) goes high (indicatingoccupancy), the base of Darlington pair Q4 (node 441) also goes high.This causes the emitter of Q4 to go high (because Q4 is an emitterfollower), but less high by about two emitter voltage drops of about 1.2volts. Timing capacitor C3 then charges up. If either or both switchesSW1A and SW1B are closed (e.g., by a user modifying the time period oftimer circuit 400), timing capacitors C1, C2, or both will also chargeup. The voltage on the timing capacitors turns ON transistor Q5. Thiscauses transistor Q6 to turn ON, assuming that the occupancy sensor isON (e.g., switch 112 of sensor 100 is set in AUTO mode, or SW2 of FIG. 8is in the up (AUTO) position, which connects the collector of Q6 toV_(BAT) via node 435). Transistor Q6 then turns ON rapidly because offeedback resistors R18 and R21. This causes the collector of transistorQ6 to suddenly rise, turning emitter follower Q7 ON. This puts theupper-rail voltage on relay driver capacitors C20 and C21 (of FIG. 5)via node 437. When the one or more timing capacitors discharge (throughresistors R17 and conducting transistor Q5), transistors Q5 and Q6rapidly turn OFF. The falling collector of transistor Q6 turns OFFtransistor Q7 and turns ON transistor Q8. This puts the lower-railvoltage on relay driver capacitors C20 and C21. Note that resistors R18and R21 provide a feedback path that turns transistors Q5 and Q6 ON andOFF more rapidly.

Advantageously, when capacitors C1, C2, and C3 are not charged (i.e.,when occupancy is not being sensed, also referred to as standby mode),timer circuit 400 draws no current.

The selection of either timing capacitors C1, C2, both, or neither viaswitches SW1A and SW1B produces four different timing intervals. Ifvalues for capacitors C1, C2, and C3 are about 22 μf, 15 μf, and 1 μf,respectively, and if values for resistors R17, R18, R21, and R23 areabout 10M ohms, 10M ohms, 4.7M ohms, and 220 k ohms, respectively, timeperiods between about 30 seconds and about 20 minutes can be selected. Aperson can thus leave a sensed area and return within the selected timeperiod without having the lights or other electrical devices orappliances abruptly turned off. Alternatively, of course, timing circuit400 can have other configurations of switches and capacitors and valuesthereof to provide other numbers of timing intervals and intervaldurations. For example, a rotary switch can be used (instead of switchesSW1A and SW1B) with the three capacitors to provide three differenttiming intervals.

Optional photocell circuit 440 inhibits sensor operation if there issufficient daylight in the sensed area. Photocell circuit 440 preferablyincludes resistor R24, potentiometer P1, photocell Z2, and diode D1, andoperates preferably as follows: when timer circuit 400 is OFF (i.e., thetiming capacitors are not charging or discharging), node 439 is low. Ifpotentiometer P1 is set low enough and if sufficient light is onphotocell Z2 to lower Z2's variable resistance enough, the base ofDarlington pair Q4 is held low (e.g., near the sensor's internalground). This prevents Q4 from accepting occupancy signals (i.e., fromturning ON). If the occupancy sensor is sensing occupancy, node 439 ishigh and the reversed biased diode D1 prevents the photocell circuitfrom influencing whether or not the sensor can process occupancysignals.

FIG. 5 shows an exemplary embodiment of a relay driver in accordancewith the invention. Relay driver 500 is preferably a latching relayrequiring about 10 milliseconds of pulse current in one polarity tocause the relay contacts to close and the same type of pulse in theother polarity to cause the relay contacts to open. The pulse amplitudeand duration are preferably what the relay manufacturer requires forreliable operation and no more. Relay driver 500 preferably includescapacitors C20 and C21; resistors R25-R30; NPN transistors Q9, Q12, Q14,and Q16; PNP transistors Q10, Q11, Q13, and Q15; NAND gates 542-545; andrelay coil 548. Transistors Q9-Q16 are arranged to produce very highcollector currents with very little input base current. They saturatesubstantially completely, allowing virtually all pulse current to enterrelay coil 548. Advantageously, relay driver 500 draws a negligibleamount of current in view of the total current drawn by an occupancysensor of the invention.

NAND gates 542-545 can be, for example, either the 4001 or 4011two-input quad logic chip, available from many chip manufacturers. NANDgates 542-545 operate on preferably about 3 volts or less and draw nearzero current. Note that the NAND logic function is not required. Otherlogic gates, such as NORs or inverters, can be used instead providedthat they preferably draw no current in standby mode and near zerocurrent when switching, have very high input impedance, very low outputimpedance, and switch rapidly.

Relay driver 500 operates preferably as follows: when capacitor C20receives the upper-rail voltage at node 437 from timer circuit 400 (orother circuit or source that generates signals indicating occupancy),C20 does nothing because its other side is at the upper rail (e.g.,V_(BAT)). However, the upper-rail voltage at node 437 causes the outputof NAND gate 543 to go low for the R-C duration of capacitor C21 andresistor R26. This output turns transistor Q10 ON, which turnstransistor Q15 ON. Upper-rail voltage is now at node 547, to which oneterminal of relay coil 548 is coupled. The low output of NAND gate 543also causes the output of NAND gate 545 to go high, which turnstransistor Q12 ON. This turns transistor Q16 ON. Node 549, to which theother terminal of relay coil 548 is coupled, goes down to about thesensor's internal ground voltage. Relay coil 548 now transfers the relaycontacts to the ON position (i.e., the closed-circuit state).

When capacitors C20 and C21 receive the lower-rail voltage (e.g., whenthe timing interval of timer circuit 400 expires), capacitor C20 andresistor R25 produce a negative pulse that activates NAND gate 542 forthe same R-C time constant (capacitor C21 and resistor R26), causing itsoutput to go high. This turns transistor Q9 ON, which turns transistorQ14 ON. Node 547 goes down to about the sensor's internal groundvoltage. NAND gate 542's high output also causes the output of NAND gate544 to go low, turning transistor Q11 ON. This turns transistor Q13 ON,which brings node 549 up to about V_(BAT). Relay coil 548 now transfersthe relay contacts to the OFF position (i.e., the open-circuit state).

FIG. 6 shows an exemplary embodiment of a relay output circuit inaccordance with the invention. Relay output 600 has relay outputcontacts 605 and 607 and a switch (e.g., armature) 650, and can be, forexample, a G6C power PCB relay manufactured by Omron Electronics LLC, ofSchaumburg, Ill. Output contacts 605 and 607 are typically connected toelectrical conductors for connection to a load and a load power source.Advantageously, either contact can be coupled to the load while theother can be coupled to the load power source, because they areelectrically interchangeable. This virtually eliminates wiring errorsduring installation.

Armature 650 is operated by relay driver 500. In particular, relay coil548 drives armature 650 to connect and disconnect contacts 605 and 607to and from each other. Thus, for example, if one contact is coupled toroom lighting and the other contact is coupled to AC line voltage, thesensing of occupancy by an occupancy sensor of the invention generatesan occupancy signal in sensing circuit 300 setting timer circuit 400,which causes relay driver 500 via relay coil 548 to transfer armature650 to the ON position, closing the connection between contacts 605 and607. AC voltage is now coupled to the room lighting, turning the lightsON. When occupancy is no longer sensed, timer circuit 400 times-out,which causes relay driver 500 via relay coil 548 to transfer armature650 to the OFF position, opening the connection between contacts 605 and607. AC voltage is now decoupled from the room lighting, turning thelights OFF.

FIG. 7 shows an exemplary embodiment of an energy storage device circuitin accordance with the invention. Energy circuit 700 includes inputs 751and 753 between which an energy storage device 760 is connected in orderto power occupancy sensor circuits. Energy storage device 760 ispreferably a single-cell battery, but can alternatively be, for example,a capacitor or fuel cell having suitable holding, current, and voltagecapabilities. Device 760 is preferably non-rechargeable and preferably a3.6 volt, 2100 mA hour, lithium non-rechargeable battery (preferably foruse with embodiments of the invention in which opamps 326 and 328 drawat most about 7 microamps each). Such a battery can be obtained from,for example, Tadiran U.S. Battery Division, of Port Washington, N.Y.Alternatively, energy storage device 760 can be a 3.6 volt, 5200 mAhour, lithium non-rechargeable battery, or two of the above 2100 mA hourbatteries preferably for use with those embodiments of the invention inwhich opamps 326 and 328 draw up to about 15 microamps each.

Energy circuit 700 preferably also includes capacitors C4 and C5.Capacitors C4 and C5 provide a lower effective impedance than theimpedance of battery 760 alone. A lower effective impedance enablesbattery 760 to maintain a higher voltage when large amounts of currentare demanded from it, such as when pulse current is applied to the relaycoil. In one embodiment of energy circuit 700, capacitors C5 and C4 areeach about 220 μf.

Energy circuit 700 preferably further includes a resistor R43. ResistorR43 is preferably of low value and, in standby mode, current throughresistor R43 is no more than about 30 microamperes, preferably no morethan about 15 microamperes, and more preferably no more than about 5microamperes. In one embodiment of energy circuit 700, resistor R43 ispreferably about 33 ohms.

FIG. 8 shows an exemplary embodiment of an optional LED circuit inaccordance with the invention. LEDs (light emitting diodes) aretypically used in occupancy sensors to indicate when occupancy is beingsensed. They do so by illuminating. However, because LEDs consumerelatively large amounts of current, limiting their operation isadvantageous. In accordance with the invention, a user can manuallyactivate LED circuit 800 for a limited period of time by setting amanual override switch (e.g., override switch 112 of sensor 100 shown inFIG. 1) to OFF and then back to AUTO. The user can then test theoperation of the sensor by stepping in and out of the sensor's field ofview and observing whether the LED illuminates or not. After the limitedperiod of time expires, LED circuit 800 automatically deactivates, thussaving power.

LED circuit 800 preferably includes manual override switch SW2,resistors R31-R40, capacitors C11 and C22-C24, NPN transistors Q17-Q19,PNP transistor Q20, and LED LT1. In normal sensor operation, switch SW2is in AUTO mode, which is the up position in FIG. 8, wherein LED circuit800 is inactive. To activate LED circuit 800, switch SW2 is moved to thedown position as shown, which is OFF mode, and then back to AUTO mode.The sensor will not respond to occupancy in OFF mode, because switch SW2disconnects V_(BAT)(via node 435) from the collector of timing circuittransistor Q6 (FIG. 4). Moving switch SW2 to OFF mode puts a positivepulse into the base of transistor Q17, turning it ON. Capacitor C11 thendischarges through transistor Q17, which turns transistor Q18 OFF.Transistor Q19 can now accept pulses from capacitor C24 each time asignal indicating occupancy is received at node 333 (e.g., from sensingcircuit 300). When transistor Q19 turns ON, it causes transistor Q20 toturn ON, which turns LED LT1 ON for the pulse duration determined by theR-C time constant of resistor R36 and capacitor C24. Regardless ofwhether SW2 is left in OFF mode (the down position) or returned to AUTOmode (the up position), transistor Q17 remains OFF allowing resistor R35to charge capacitor C11. When the voltage on capacitor C11 issufficiently high, transistor Q18 turns ON, which turns transistor Q19OFF. Transistor Q19 is now prevented from receiving any more pulses fromsensing circuit 300 (i.e., is prevented from turning ON). Thus, LED LT1remains active for the time period determined by the R-C time constantof resistor R35 and capacitor C11. Advantageously, LED circuit 800 drawsminute current from energy storage device 760 when the LED isdeactivated, and very little of the total sensor current while the LEDis active during those limited periods of time.

FIG. 9 shows an exemplary embodiment of an optional lock-out circuit inaccordance with the invention. Lock-out circuit 900 locks out signalsindicating occupancy generated by sensing circuit 300 for about 500milliseconds after timer circuit 400 times-out. This prevents sensingcircuit 300 from mistakenly generating an occupancy signal in responseto relay contact arcing. Relay contact arcing can occur when thearmature opens the connection between the relay output contacts.

Lock-out circuit 900 preferably includes resistors R41 and R42,capacitor C25, NPN transistor Q21, and diode D2, and operates preferablyas follows: when the relay driver OFF pulse appears at the base oftransistor Q9 (FIG. 5), it charges up capacitor C25 via node 546.Capacitor C25 then turns transistor Q21 ON for preferably about a halfsecond. The base of Darlington pair Q4 (FIG. 4), which is connected tothe collector of transistor Q21 via node 441, is held at the sensor'sground for this short duration. This prevents any occupancy signalsgenerated by sensing circuit 300 from propagating through timer circuit400 during that half second.

Note that at least some of the circuits described above, or portions ofthem, are not limited solely to use in occupancy sensors, butalternatively can be used in other devices, such as, for example, dataloggers and proximity sensors.

Thus it is seen that self-powered long-life occupancy sensors and sensorcircuits are provided. One skilled in the art will appreciate that theinvention can be practiced by other than the described embodiments,which are presented for purposes of illustration and not of limitation,and the invention is limited only by the claims which follow.

1. A method of coupling a first relay output to a second relay outputbased on occupancy sensed within a designated area, said methodcomprising: sensing occupancy within said designated area; generating asignal indicating occupancy in response to said sensing; and couplingsaid first and second relay outputs to each other using an armatureoperative to couple AC line voltage with no more than about 3 voltssupplied to a latching relay circuit that generates a single electricalpulse in response to the generated signal, the 3 volts providedexclusively by a non-rechargeable battery.
 2. The method of claim 1wherein said coupling comprises coupling said first and second relayoutputs to each other using a relay coil powered by no more than about 3volts supplied by a non-rechargeable battery in response to saidgenerated signal.
 3. The method of claim 1 wherein said non-rechargeablebattery supplies no more than about 3-6 volts.
 4. The method of claim 1wherein said first relay output is operative to be coupled to a load andsaid second relay output is operative to be coupled to power for saidload.
 5. The method of claim 1 wherein said generating comprisesamplifying a signal indicating occupancy using no more than about 30microamperes of current supplied by said non-rechargeable battery inresponse to said sensing.
 6. The method of claim 1 further comprising:activating a timer for a limited period of time in response to saidgenerated signal; decoupling said first and second outputs from eachother in response to said limited period of time expiring; and poweringsaid generating, said activating, and said decoupling with saidnon-rechargeable battery.
 7. The method of claim 1 further comprising:illuminating a light emitting diode in response to said generatedsignal; and powering said sensing, said generating, and saidilluminating with said non-rechargeable battery.
 8. The method of claim1 further comprising enclosing said non-rechargeable battery, saidsensing, said generating, and said coupling in a single housing.
 9. Amethod of coupling a first relay output to a second relay output basedon occupancy sensed within a designated area, said method comprising:sensing occupancy within said designated area; generating a signal to atimer, wherein the signal indicates occupancy in response to saidsensing; activating the timer for a limited period of time in responseto said generating a signal; applying a voltage pulse of a firstpolarity across a relay coil in response to said activating; couplingsaid first and second relay outputs to each other with no more thanabout 3 volts supplied by a non-rechargeable battery in response to saidgenerated signal; applying a second voltage pulse of a second polarityacross said relay coil in response to said limited period of timeexpiring; decoupling said first and second relay outputs from each otherin response to said applying a second voltage pulse; and powering saidtimer and said relay coil with said non-rechargeable battery. 10.Apparatus for coupling a first relay output to a second relay outputbased on occupancy sensed within a designated area, said apparatuscomprising: means for sensing occupancy within said designated area;means for generating a signal indicating occupancy in response tosensing occupancy; and means for coupling said first and second relayoutputs to each other using an armature operative to couple AC linevoltage with no more than about 3 volts supplied to a latching relaycircuit that generates a single electrical pulse in response to thegenerated signal, the 3 volts provided exclusively by a non-rechargeablebattery.
 11. The apparatus of claim 10 further comprising: means forcoupling said first relay output to a load; and means for coupling saidsecond relay output to power for said load.
 12. The apparatus of claim10 wherein said means for generating comprises means for amplifying asignal indicating occupancy using no more than about 30 microamperes ofcurrent supplied by said non-rechargeable battery in response to saidsensing.
 13. The apparatus of claim 10 further comprising means forilluminating a light emitting diode in response to generating a signal.14. The apparatus of claim 10 further comprising means for enclosingsaid non-rechargeable battery, said means for sensing, said means forgenerating, and said means for coupling.
 15. The apparatus of claim 14wherein said means for enclosing comprises a single housing.
 16. Theapparatus of claim 10 wherein said means for coupling comprises a relaycoil.
 17. The method of claim 9 further comprising: coupling said firstrelay output to a load; and coupling said second relay output to powerfor said load.
 18. The method of claim 9 wherein said generatingcomprises amplifying a signal indicating occupancy using no more thanabout 30 microamperes of current supplied by said non-rechargeablebattery in response to said sensing.
 19. The method of claim 9 furthercomprising illuminating a light emitting diode in response to saidgenerated signal.
 20. The method of claim 9 further comprising enclosingsaid non-rechargeable battery, said sensing, said generating, and saidcoupling in a single housing.